In the design of transmission, particularly heavy duty transmissions such as used on trucks, there has existed for a long time the problem of shifting the transmission through the various speed ratios, which problem is even greater when the transmission is provided with an auxiliary or range transmission section for increasing the number of speed ratios. In most known transmissions, the shifting process is either relatively difficult and/or the shifting mechanism is relatively complex. Thus, there has been a continuing effort in the design of transmissions to improve the shifting, to improve the rapidity of shifting, to reduce the complexity of the shifting mechanism and to reduce its cost. Hence, without detracting from the operability or desirability of many of the shifting mechanisms previously known, it may be stated that in the present invention these general objectives are accomplished to even a greater degree than has been previously possible.
Particularly, most known transmissions have necessarily utilized synchronizers, of which many different types are known, for causing the speed of the jaw or toothed clutch members to be substantially synchronized prior to permitting their interengagement during a shifting sequence from one speed ratio to another speed ratio. While the use of synchronizers does permit the shifting operation to be performed, their use, as is already known, imposes certain requirements of weight, space and power which it is desirable to ease, or avoid entirely, if possible.
These and other problems incident to previously known transmissions were set forth and acknowledge in my application Ser. No. 276,376 now U.S. Pat. No. 3,799,002, issued Mar. 26, 1974 entitled "Transmission with Resiliently Loaded Main Shaft Gears" assigned to the same assignee as the present application and apparatus was disclosed therein which effectively meets these problems while providing a reliable, effective and efficient transmission, particularly for heavy duty use.
While both forms of the invention disclosed in said application, namely that using blockers and that not using blockers, are effective for carrying out the objectives thereof, it has been noted that for the usual reasons both noise and clutch tooth wear can be minimized by the use of blockers as set forth in said application and since the date thereof a considerable amount of further investigation has been carried out related thereto, both for the simplifying of the blocker structure and for improving the operation thereof.
In this last connection, it was noted in the further development of the embodiment shown in said application using blockers that sometimes after a period of neutral condition with the vehicle stopped it was impossible to shift the auxiliary transmission in an upshift direction. This could usually be cured by first shifting momentarily from neutral into reverse, but this obviously was an inconvenient and a highly undesirable technique and it appreciably hampered the commercial acceptability of an otherwise highly satisfactory transmission.
In further development and study of this transmission, particularly with respect to the problem just named, it was discovered that said problem occurred when the front box of the transmission came into neutral with the vehicle stopped and an upshift selected. Because of the previous mode of operation in a lower gear, the blocker can be unblocked for such upshift only by reducing the speed of the main shaft which here, since it is in the case in question already stopped, can be accomplished only, as above noted, by momentarily reversing the main shaft.
In addition it was noted that during a compound shift the change in speed of the main shaft caused by the other member involved in the sequence can cuase inertia forces exceeding the random contact forces on the blocker. This causes the blocker to change position during the interval while the shaft is changing speed. When the second member of the sequence starts to move into position under this condition, the blocker immediately unblocks resulting in an undesirable pre-synchronous shift.
Accordingly it is an object of the present invention to provide a transmission having improved shifting structure for overcoming the above-mentioned disadvantages. Particularly, it is an object of the present invention to provide:
1. A transmission having means to improve the ease of shifting, to improve the rapidity of shifting without requiring large synchronizers, to reduce complexity of the mechanism and to reduce its cost.
2. A transmission, as aforesaid, which utilizes resilient means for causing meshing engagement of the jaw clutch members after the desired speed synchronization has been achieved.
3. A transmission, as aforesaid, having the main shaft gears floatingly supported relative to the main shaft by a plurality of countershaft gears so as to minimize the inertia of the main shaft and including clutch collars keyed to the main shaft for cooperation of the main shaft gears.
4. A transmission, as aforesaid, utilizing blockers for assisting in effecting a smooth and noise-free shift and particularly for minimizing the wear on the inter-engaging jaw clutch teeth.
5. To provide a transmission, as aforesaid, wherein the previously existing above-described tendency to require momentary reverse operation before shifting out of an idling condition is eliminated.
6. To provide blockers of such structure in relationship to other components of the transmission as to eliminate the above-mentioned previously existing tendency for erroneous positioning of such blockers with respect to the clutch components.
7. To provide a transmission and blocker arrangement wherein the blockers on the main shaft part of a jaw clutch will be subjected to sufficient axial drag as to cause same to bear against the gear cone and thus effect a rotative force exceeding the inertia forces occurring thereon and thereby to effect a proper positioning thereof.
8. To provide a blocker construction of simplified but yet stronger construction than previously known blockers of this general type and nature.
Other objects and purposes of the invention will become apparent to persons acquainted with devices of this type upon reading the following specification and inspecting the accompanying drawings.